California’s plan to pay for construction of the $64-billion bullet train has many unanswered questions and shaky assumptions, senators from across the state told rail officials Monday.

“We want you to beef up your financing package,” Sen. Jim Beall (D-San Jose), a longtime supporter of the high-speed project, said at a hearing of the Senate Transportation and Housing Committee, which he chairs.

Republican lawmakers were even tougher. “I think the financing is shaky here,” said Sen. Jim Nielsen (R-Gerber). “It seems like it is careening down the tracks.”

The committee was responding to a draft business plan the California High-Speed Rail Authority released in February. The authority said …